Two-stage ac-dc power converter with buck pfc and improved thd

Abstract

A two-stage AC-DC power converter for powering a load at a substantially constant current, and related methods and systems. The first or front end stage of the AC-DC power converter includes a buck topology power factor correction (PFC) circuit and a PFC controller. The second stage of the AC-DC power converter includes a conventional isolation and regulator circuit configured to receive the DC voltage and DC current output by the buck PFC and then to provide the substantially constant current to the load. By multiplying the rectified input voltage sensed by the PFC controller, the input AC current drawn by the buck PFC circuit has a much improved total harmonic distortion (THD), which is achievable without the need for using an expensive PFC controller. The rectified input voltage sensed by the PFC controller is multiplied using a Zener diode ladder.

What is claimed is: 
     
         1 . An AC-DC power converter for powering a load at a substantially constant current, comprising:
 a buck topology power factor correction (PFC) circuit, the buck PFC circuit having a PFC controller, the buck PFC circuit configured to draw an alternating current (AC) input current having a first total harmonic distortion (THD), the PFC controller configured to sense a rectified input voltage from a full-wave rectifier, the PFC circuit outputting a direct current (DC) voltage and a DC current;   a downstream isolation and regulator circuit configured to receive the DC voltage and the DC current output by the buck PFC circuit and to provide the substantially constant current to the load; and   a passive voltage multiplier circuit configured to multiply the rectified input voltage sensed by the PFC controller, whereby multiplying the rectified input voltage sensed by the PFC controller causes the input AC current drawn by the buck PFC circuit to have a second, improved THD.   
     
     
         2 . The AC-DC power converter of  claim 1 , wherein the passive voltage multiplier circuit comprises a Zener diode ladder having a number of Zener diode-resistor pairs, wherein the Zener diode ladder approximates a polynomial function for multiplying the rectified input voltage sensed by the PFC controller, the polynomial function defined as X n , where “n” is a real number corresponding to the number of Zener diode-resistor pairs in the Zener diode ladder. 
     
     
         3 . The AC-DC power converter of  claim 2 , wherein the input AC current having the second, improved THD is defined by the equation: Ip(t)=K*Vg n (t). 
     
     
         4 . The AC-DC power converter of  claim 1 , wherein the passive voltage multiplier circuit is part of the buck PFC circuit and wherein the buck PFC circuit is configured to operate in transition mode. 
     
     
         5 . The AC-DC power converter of  claim 1 , wherein the AC-DC power converter is a two-stage AC-DC power converter, wherein the buck PFC circuit is a first stage of the two-stage AC-DC power converter and wherein the downstream isolation and regulator circuit is a second stage of the two-stage AC-DC power converter. 
     
     
         6 . The AC-DC power converter of  claim 1 , wherein the downstream isolation and regulator circuit includes a low voltage flyback circuit, wherein the amperage of the substantially constant current provided to the load is set according to a configuration of the low voltage flyback circuit. 
     
     
         7 . The AC-DC power converter of  claim 1 , wherein the full wave rectifier is coupled to an AC power supply and wherein the second, improved THD of the input AC current is lower than the first THD and wherein the second, improved THD enables the two-stage AC-DC power converter to draw less current from the AC power supply. 
     
     
         8 . A method for powering a load at a substantially constant current using a two stage AC-DC power converter, comprising:
 providing alternating current (AC) power to a first stage of the AC-DC power converter, the first stage including a buck topology power factor correction (PFC) circuit and a PFC controller, the first stage of the AC-DC power converter drawing an input AC current having a first total harmonic distortion (THD);   providing a direct current (DC) voltage and a DC current output from the first stage to a second stage of the AC-DC power converter, the second stage of the AC-DC power converter including a downstream isolation and regulator circuit that provides the substantially constant current to the load;   generating a rectified input voltage from the AC power supply;   multiplying the rectified input voltage; and   sensing the multiplied rectified input voltage at the PFC controller, thereby causing the input AC current drawn by the first stage of the AC-DC power converter to have a second, improved THD.   
     
     
         9 . The method of  claim 8 , wherein the step of multiplying the rectified input voltage is accomplished using a passive voltage multiplier circuit configured as a Zener diode ladder having a plurality of Zener diode-resistor pairs, each respective Zener diode-resistor pair including a Zener diode in parallel with a corresponding resistor, wherein the Zener diode ladder approximates a polynomial function for multiplying the rectified input voltage sensed at the PFC controller, the polynomial function defined as X n , where “n” is a real number corresponding to the number of Zener diode-resistor pairs in the Zener diode ladder. 
     
     
         10 . The method of  claim 8 , wherein the step of sensing the multiplied rectified input voltage at the PFC controller comprises providing the multiplied rectified input voltage to a voltage sensing input of the PFC controller. 
     
     
         11 . The method of  claim 8 , wherein the downstream isolation and regulator circuit includes a low voltage flyback circuit, further comprising the step of setting the amperage of the substantially constant current provided to the load based on configuration settings of the low voltage flyback circuit. 
     
     
         12 . A system for powering a load at a substantially constant current, comprising:
 an alternating current (AC) power supply that provides an input AC voltage and an input AC current;   a full-wave rectifier coupled to the AC power supply that converts the AC input voltage into a rectified input voltage;   a first stage of a two stage AC-DC power converter, the first stage including a buck topology power factor correction (PFC) circuit operating in transition mode and a PFC controller, the buck PFC circuit configured to draw the input AC current from the AC power supply at a first total harmonic distortion (THD), the PFC controller having an input for receiving the rectified input voltage from the full-wave rectifier, the PFC circuit outputting a direct current (DC) voltage and a DC current;   a second stage of the two stage AC-DC power converter, the second stage including a downstream isolation and regulator circuit configured to receive the DC voltage and the DC current output by the buck PFC circuit and to provide the substantially constant current to the load; and   a passive voltage multiplier circuit positioned between the full-wave rectifier and the input of the PFC controller, the passive voltage multiplier circuit configured to multiply the rectified input voltage sensed by the input of the PFC controller, whereby multiplying the rectified input voltage sensed by the input of the PFC controller causes the input AC current drawn by the buck PFC circuit to have a second, improved THD.   
     
     
         13 . The system of  claim 12 , wherein the passive voltage multiplier circuit comprises a Zener diode ladder that includes a plurality of Zener diode-resistor pairs, each respective Zener diode-resistor pair including a Zener diode in parallel with a corresponding resistor, wherein the Zener diode ladder approximates a polynomial function for multiplying the rectified input voltage sensed at the PFC controller, the polynomial function defined as X n , where “n” is a real number corresponding to the number of Zener diode-resistor pairs in the Zener diode ladder. 
     
     
         14 . The system of  claim 13 , wherein the input AC current having the second, improved THD is defined by the equation: Ip(t)=K*Vg n (t). 
     
     
         15 . The system of  claim 13 , wherein the downstream isolation and regulator circuit includes a low voltage flyback circuit and wherein the amperage of the substantially constant current provided to the load is set according to a configuration of the low voltage flyback circuit. 
     
     
         16 . An improved AC-DC power converter, the AC-DC converter configured to receive a rectified input voltage from a bridge rectifier, the bridge rectifier being coupled to an alternating current (AC) power supply that provides an input AC voltage and an input AC current, comprising:
 a buck topology power factor correction (PFC) circuit, the buck PFC circuit having a PFC controller and configured to draw the input AC current, the input AC current having a first total harmonic distortion (THD), the PFC controller configured to sense the rectified input voltage, the PFC circuit outputting a direct current (DC) voltage and a DC current; and   a passive voltage multiplier circuit configured to multiply the rectified input voltage sensed by the PFC controller, whereby multiplying the rectified input voltage sensed by the PFC controller causes the input AC current drawn by the buck PFC circuit to have a second, improved THD.   
     
     
         17 . The AC-DC power converter of  claim 16 , wherein the passive voltage multiplier circuit is a passive voltage squarer circuit comprising a Zener diode ladder, wherein the Zener diode ladder includes a plurality of Zener diode-resistor pairs, and wherein the Zener diode ladder approximates a polynomial function for multiplying the rectified input voltage sensed by the PFC controller, the polynomial function defined as X″, where “n” is a real number corresponding to the number of Zener diode-resistor pairs in the Zener diode ladder. 
     
     
         18 . The AC-DC power converter of  claim 16 , wherein the passive voltage multiplier circuit is positioned between the bridge rectifier and the PFC controller. 
     
     
         19 . The AC-DC power converter of  claim 16 , wherein the passive voltage multiplier circuit provides the multiplied rectified input voltage to a voltage sensing input of the PFC controller. 
     
     
         20 . The AC-DC power converter of  claim 16 , wherein the buck PFC circuit is configured to operate in transition mode.